Persistent organic pollutants, aka POPs, are a class of carbon-based chemicals that are resistant to environmental degradation. They are named for this ability to stay in the environment for long periods of time, if not indefinitely. They traverse from one organism to another via the food chain (and the process of biomagnification!) and so, similar to heavy metals, these toxic substances are often found in the fat tissues of animals and humans. 

The production of POPs exploded in the early 1950s, following the post-World War II industrial revolution. Thousands of synthetic chemicals were introduced for commercial purposes, supporting pest and disease control as well as crop production. Eventually, researchers discovered the harmful effects these chemicals had on human health and the environment, resulting in the ban of certain POPs (including polychlorinated biphenyls, or PCBs, in the 1970s).

Fast forward to the 1990s — the Governing Council of the United Nations Environment Programme (UNEP) called for a global response to POPs in 1995. The council formed an international working group that analyzed data around key POPs of interest and proposed a plan of action. 

In May 2001, 152 countries signed the Stockholm Convention, a groundbreaking treaty intended to address this global concern. By signing this environmental treaty, each country committed to reducing or eliminating the production, use, and release of the “dirty dozen” — 12 key POPs that had been identified by that time. This list has since grown to 28 chemicals and counting.

Despite global mandates, POPs persist in the environment and are regularly found in animals and humans alike, so it’s important to understand the risk and impact they introduce. Today, we’re uncovering the history and health effects of POPs, aka the reason why the latest labels you should be checking are on your furniture.

What Are Persistent Organic Pollutants and Why Should I Care?

POPs are a class of synthetic chemicals

POPs are a class of man-made compounds, including many pesticides and industrial chemicals, that have been used extensively since the 1940s. The most notorious pollutants include polychlorinated biphenyls (PCBs), which are widely used in plastic products and electric equipment, and the pesticide dichlorodiphenyltrichloroethane (DDT), which in some countries is still used as protection against malaria, typhus, and other diseases spread by insects. POPs are typically broken up into two key categories: 1) intentionally produced chemicals currently or previously used in agriculture, pest control, or industrial processes, and 2) unintentionally produced POPs that result from industrial processes or combustion (even forest fires!), such as dioxins. POPs can accumulate in the body, causing adverse health effects at low concentrations. (Source)

POPs can remain in the environment for long periods of time

POPs are found in every corner of the globe, including water, soil, food, and the air. As their name suggests, POPs persist in the environment — they’re resistant to natural degradation and do not break down easily. They can travel long distances quickly (via oceans, rivers, lakes or with the help of migratory species), accumulate in the fatty tissue of humans and wildlife, and increase in concentration up the food chain, which makes it difficult to control their spread and limit their impact. On top of that, it can be difficult to trace the movement of most POPs in the environment because these compounds can exist in different phases (e.g., as a gas or attached to airborne particles). (Source, Source, Source)

POPs are extremely hazardous

POPs pose a significant threat to wildlife — exposure has been linked to adverse immune system effects, reproductive disorders, and population decline in birds, fish, and other wildlife species. In humans, POPs have been linked to reproductive, developmental, behavioral, neurologic, endocrine, and immunologic health effects. The main source of exposure for humans is through contaminated foods. Less commonly, humans are exposed through contaminated drinking water and direct contact with chemicals. POPs can be transferred to offspring through placenta and breast milk in all mammals. However, the known benefits of breastfeeding still outweigh the suspected risks of exposure (remember how critical it is for the gut microbiome formation in the early days?). (Source, Source)

Some POPs are still used in the US

Although a number of POPs have been banned, many — including organochlorine pesticides and certain types of polybrominated diphenyl ethers (PBDEs) — continue to be produced in the United States. PBDEs are toxic industrial flame retardant chemicals used in consumer electronics, furniture, and mattresses. Although many states have since banned the production of various forms of these chemicals, articles containing some of them can still be imported into the US. Similar to other POPs, some of these PBDEs are still being detected in humans and the environment, with some reports indicating that levels are actually increasing. (Source, Source)

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A diagram of how POPs affect our waters. (Source)

What Does the Research Show About Persistent Organic Pollutants?

POPs are neuro-developmental toxicants

Research has shown that PCBs and other POPs can cross the blood–brain barrier of immature animals, including humans, and are associated with adverse effects on early brain development. Exposure to POPs in the womb is linked to lower birth weights, smaller head circumferences, and increased incidence of congenital malformations. (Source, Source)

POPs can disrupt the endocrine system

Accumulating evidence suggests that POPs have toxic effects on the endocrine system. Perfluorinated compounds (PFCs) interfere with the iodine receptors in the thyroid gland affecting function. Thyroid hormones regulate metabolic processes in all cells of the body, and disruptions to these hormones can cause weight gain, mood changes, depression, and cognitive impairment. Low thyroid levels in pregnancy can affect not only the mother but also her baby, resulting in preterm birth, low birth weight, or impairment of intelligence and learning ability. (Source, Source)

POPs have been linked to diabetes

DDE (a byproduct of DDT) is a suspected human carcinogen that disrupts the immune and endocrine systems, and is strongly linked to the development of type 2 diabetes. Researchers have deemed DDE a risk factor after finding a relationship between high levels of DDE and high fasting blood sugar levels in adults, as well as increased insulin resistance in mice. Researchers are still investigating how POPs may play a role in diabetes but believe potential mechanisms may involve alterations to lipid metabolism, glucose transport, and the insulin signaling pathway. (Source, Source, Source, Source)

The Great Lakes raised a red flag about POPs

Research conducted in the Great Lakes region has informed much of our understanding of POPs, at-risk populations, and possible health effects. Back in the 1970s, studies found a correlation between fish consumption and elevated serum POPs in people living  in this region, leading researchers to conclude eating contaminated fish is a form of human exposure to POPs. (Source)

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So What Should I Do About Persistent Organic Pollutants?

Opt for wild fish over farmed

A survey in the Journal of Science compared levels of organochlorine contaminants, including PCBs and dioxins, in farmed and wild salmon from around the globe and found higher amounts in the farmed salmon. These levels for farmed fish typically represent how contaminated the feed is for farmed fish. Based on this, experts suggest that consumers limit farmed salmon to fewer than 10 meals per month. According to the Environmental Working Group (EWG), among fish, farmed salmon, trout, sardines, catfish, herring, and bluefish are the species with the high concentrations of POPs, although no formal studies exist yet to confirm this. (Source, Source, Source, Source) 

Choose lean meats and fish over animal foods with high fat content

Given that POPs are largely retained in fat tissue, the concentration of POPs in dairy and meat products is closely related to fat content or percentage. POPs are present in both conventionally raised and organic meat and dairy products — beef, goat, sheep/lamb, bison, cow milk, sheep milk, and goat milk all score high for POPs. Pork, chicken, and eggs tend to have lower concentrations. Another pro tip is to cut off visible fat from meat and poultry before cooking. Preparation of your proteins can be key, too — skip the fried fish, as frying seals in pollutants that might be in the fish's fat. Grilling or broiling are great cooking alternatives, because they allow the fat to drain away. (Source)

Maintain a healthy body weight

In addition to the many other benefits of staying at a healthy weight, it can be a good idea when it comes to POPs. Since POPs are stored in fat tissue, these stores can release POPs into the bloodstream causing continual exposure and harm even if measures are taken to reduce intake of POP-contaminated foods. (Source)

Make sure your furniture is PBDE-free

Most furniture sold in the US conforms to California’s laws regarding fire safety, which discourages, but does not forbid, the use of flame retardants. However, while some manufacturers may state on the label whether or not the item contains retardants, this is not required. So whether you’ve had your sofa for years or are shopping for a new one, be sure to check the labels or ask the manufacturer. If you find your furniture may contain PBDEs, consider looking for an upholstery business that can replace the foam in the cushions, since that’s where most retardants are concentrated. (Source)

Test your water for POPs

POPs and other chemicals can linger in our water, so you should investigate the status of your H2O, especially if you’re on well water. You can buy kits online for DIY tap testing, but as a heads up, it’s not always clear what they test for or how accurate their results are. The EPA recommends using a certified lab and shares a list of options on their website. If your water contains POPs above the EPA drinking water advisory levels, consider installing a filtration system such as an activated carbon or reverse osmosis system, or use water bottled in glass (we don’t need more single-use plastics!) when drinking and cooking.

Where Can I Learn More About Persistent Organic Pollutants?

For all the banned substances

If you’re curious to learn more about the initial “dirty dozen” or new chemicals added to the Stockholm Convention, you can find the entire list of prohibited chemicals here. The website also provides the most up-to-date news and information on the Convention.

For more chemical deep dives

If you’re looking for a “Rooted in Science”-like take on additional POPs and toxic chemicals, the Toxic-Free Future nonprofit answers key questions around a set of “chemicals of concern.” They cover government actions and practical tips to reduce your exposure for everything from Teflon to phthalates. (Source)